With the exploration and development of oil and gas fields in China, deep wells, ultra‑deep wells, high‑pressure wells, and corrosive wells containing hydrogen sulfide and carbon dioxide are increasing, especially in western China. The wide application of directional well and cluster well drilling technologies, as well as gas‑lift and gas‑injection production technologies, has put forward higher requirements for the service performance of tubing and casing connections. The gas‑tightness, connection strength and corrosion resistance of API round thread and buttress thread connections widely used in the past can no longer meet the requirements. The development and application of premium threaded connections for tubing and casing has become an urgent requirement for oil and gas exploration and development.
The reason why API standard threaded connections cannot adapt to harsh working conditions mainly lies in sealing and strength problems associated with thread structure and thread profile. Sealing of API standard threaded connections is realized by thread compound, thread plating and thread interference engagement, which generally only satisfy water‑tightness conditions. API threaded connections also have relatively low tensile strength. Under normal conditions, the joint tensile strength is only 80% of the pipe body strength.
Currently, there are roughly hundreds of types of premium tubing and casing connections produced and used abroad, yet only more than ten are typical and widely applied. Previously, premium‑connection tubing and casing were all imported at high prices. In recent years, a small number of domestic manufacturers have developed premium‑connection tubing and casing. Since 2002, Shengli Highland Petroleum Equipment Co., Ltd. has developed premium‑thread casing for thermal recovery wells and continuously rolled out various premium threaded products. The main products are as follows:
SL100H Premium‑Thread Casing for Thermal Recovery Wells
It adopts Cr‑Mo steel pipe with high thermal stability and high collapse resistance, and is equipped with premium threads of high tensile strength, strong thermal deformation resistance and superior gas‑tightness. It can withstand more than 9 steam‑injection operations. The service life of thermal recovery wells is more than doubled compared with wells using N80 casing, reaching the performance level of similar foreign products. It has passed full‑scale performance evaluation by Xi’an Oil Tubular Goods Research Institute and completed field tests in Shengli Oilfield.
SLT Gas‑Tight Premium‑Thread Casing (formerly SLCQ)
It adopts primary metal‑to‑metal conical sealing with precision smooth surfaces. The sealing taper is designed according to the optimal sealing angle for different casing sizes. The sealing surfaces are convenient for inspection, and gas‑tightness can be guaranteed even under severe tension and compression conditions. The torque shoulder provides auxiliary sealing with good over‑torque resistance. Dual primary and secondary metal sealing achieves better sealing effect. The inner‑bore streamline design prevents turbulence at the joint, minimizes energy loss and avoids erosion and crevice corrosion at connections. Position‑controlled make‑up ensures reliable performance under harsh tension and bending loads and facilitates field operation.
Main features:
(1) Modified API buttress thread is adopted, featuring high connection strength and improved thread interchangeability.
(2) Reversed anti‑torque shoulder locks the pipe end after casing make‑up to prevent pipe‑end diameter reduction under load.
(3) Sealing surfaces: primary conical‑to‑conical seal and secondary shoulder‑to‑shoulder seal.
‑ Position‑controlled make‑up delivers stable performance under severe tension and bending for convenient field operation.
‑ Internal torque‑stop shoulder design withstands high torque with excellent over‑torque performance.
‑ The sealing taper is optimized for different casing sizes to maintain gas‑tightness under severe tension and compression.
‑ Streamline inner‑bore profile eliminates joint turbulence, reduces energy loss and prevents joint erosion and crevice corrosion, realizing uniform interference‑fit deformation on sealing surfaces.
Currently, there are roughly hundreds of types of premium tubing and casing connections produced and used abroad, yet only more than ten are typical and widely applied. Previously, premium‑connection tubing and casing were all imported at high prices. In recent years, a small number of domestic manufacturers have developed premium‑connection tubing and casing. Since 2002, Shengli Highland Petroleum Equipment Co., Ltd. has developed premium‑thread casing for thermal recovery wells and continuously rolled out various premium threaded products. The main products are as follows:
SL100H Premium‑Thread Casing for Thermal Recovery Wells
It adopts Cr‑Mo steel pipe with high thermal stability and high collapse resistance, and is equipped with premium threads of high tensile strength, strong thermal deformation resistance and superior gas‑tightness. It can withstand more than 9 steam‑injection operations. The service life of thermal recovery wells is more than doubled compared with wells using N80 casing, reaching the performance level of similar foreign products. It has passed full‑scale performance evaluation by Xi’an Oil Tubular Goods Research Institute and completed field tests in Shengli Oilfield.
SLT Gas‑Tight Premium‑Thread Casing (formerly SLCQ)
It adopts primary metal‑to‑metal conical sealing with precision smooth surfaces. The sealing taper is designed according to the optimal sealing angle for different casing sizes. The sealing surfaces are convenient for inspection, and gas‑tightness can be guaranteed even under severe tension and compression conditions. The torque shoulder provides auxiliary sealing with good over‑torque resistance. Dual primary and secondary metal sealing achieves better sealing effect. The inner‑bore streamline design prevents turbulence at the joint, minimizes energy loss and avoids erosion and crevice corrosion at connections. Position‑controlled make‑up ensures reliable performance under harsh tension and bending loads and facilitates field operation.
Main features:
(1) Modified API buttress thread is adopted, featuring high connection strength and improved thread interchangeability.
(2) Reversed anti‑torque shoulder locks the pipe end after casing make‑up to prevent pipe‑end diameter reduction under load.
(3) Sealing surfaces: primary conical‑to‑conical seal and secondary shoulder‑to‑shoulder seal.
‑ Position‑controlled make‑up delivers stable performance under severe tension and bending for convenient field operation.
‑ Internal torque‑stop shoulder design withstands high torque with excellent over‑torque performance.
‑ The sealing taper is optimized for different casing sizes to maintain gas‑tightness under severe tension and compression.
‑ Streamline inner‑bore profile eliminates joint turbulence, reduces energy loss and prevents joint erosion and crevice corrosion, realizing uniform interference‑fit deformation on sealing surfaces.
| Size and Specifications: | |
| Casing | Tubing |
| 13-3/8" CSG, K-55, 54.5 PPF, BTC, R-3, Gas Tights, Premium Conn. | 2-7/8" Tubing L-80 6.5 ppf 13Cr, R2, Gas Tight, Premium Connection |
| 9-5/8" CSG, L-80, 43.5 PPF, R3, Gas Tights | |
| 9-5/8" CSG, L-80, 43.5 PPF, Gas Tights, 4 ft， BTC | |
| 9-5/8" CSG, L-80, 43.5 PPF, Gas Tights, 6 ft， BTC | 3-1/2" Tubing L-80 9.3 ppf 13Cr, R2, Gas Tight, Premium Connection |
| 9-5/8" CSG, L-80, 43.5 PPF, Gas Tights, 8 ft， BTC | |
| 9-5/8" CSG, L-80, 43.5 PPF, R-3, BTC | 4-1/2" Tubing L-80 12.6 ppf 13Cr, R2, Gas Tight, Premium Connection |
| 7" CSG, L-80, 13Cr, 26.00 PPF, R-3, Premium Connection | |
| 7" CSG, L-80, 13Cr, 29 PPF, R-3 Perforated Casing | |
| Pup Joint | Cross Over |
| Pup joint, 2-7/8", L-80 6.4 ppf 13Cr, Gas Tight, Premium Connection | X/O, 3-1/2" Pin X 4-1/2" Box, L-80 9.3 ppf 13Cr, Gas Tight, Premium Connection |
| Pup joint, 3-1/2", L-80 9.2 ppf 13Cr, Gas Tight, Premium Connection | X/O, 3-1/2" Box X 4-1/2" Pin, L-80 9.3 ppf 13Cr, Gas Tight, Premium Connection |
| Pup joint, 4-1/2", L-80 12.6 ppf 13Cr, Gas Tight, Premium Connection | X/O 4-1/2" Tubing L-80 12.75 ppf 13Cr PIN x PIN Gas Tight - Premium Connection |
